Lab 2 – Intro to the Grid World
Hello! Welcome to Week 2 of Artificial Intelligence. The purpose of this lab is to introduce you to the Grid World where the remaining prolog labs will take place. This lab is vitally important for both coursework and exam students so please make sure that you complete it.
You will need to use a local swipl installation in order to run this code as SWISH will not work. You are also encouraged to use a text editor of your choice to edit the files (Both VSCode and Atom have support for prolog). If you have any trouble setting up swipl then please make a post in the megathread
You are provided with library code to host the webpage, make queries to wikipedia, as well as various other functions regarding the state of the game. This is all stored inside /ailp (standing for Artificial Intelligence with Logic Programming).
You are also provided with 3 files of the form lab_*_12345.pl. This is where you will complete the exercises, and you will be pointed to the correct file for each section. Each of the files also has function stubs that you will need to implement for each of the exercises. The reason for the 12345 is because it will be replaced with your candidate number if you go on to do the coursework (alhough these labs aren’t assessed so feel free to use whatever you want).
You do not need to look into the internals of the library (although if you want to you can).
By the end of next week you will be able to do a more complex task, in a more complex grid world, as seen below.
Exercise 1: Geting Around
For this exercise you will learn how to move around the grid world and how to create a spiral and ultimately create a spiral. The grid world is just the name of the environment that these labs will take part in. For this exercise you will be editing lab_grid_12345.pl.
Possible Queries
The following queries have been exported from the library code:
Query Name Description
start Initiate the web server
shell Open the command shell
my_agent(-A) Returns the ID of your Agent
ailp_grid_size(-N) Returns the size of the grid
get_agent_position(+A,-Pos) Returns the position of Agent A
agent_do_moves(+A,+L) Makes Agent A perform the list of moves L
How to run?
THIS IS ONE OF THE MOST IMPORTANT SECTIONS. In order to run the grid world, you need to open ailp.pl using swipl. This exercise is known as lab grid so we will pass that as a command line argument (e.g. swipl ailp.pl lab grid).
Upon loading you will likely see a lot of warnings
about singleton variables. this is normal and only because the functions in lab_grid_12345.pl have not been implemented.
Next, Type in start. and hit enter to start the webserver. If you press anything but ‘N’/’n’, then the webpage will open automatically in your default browser. Hit the run button on the webpage before you continue.
We will use a shell to initialise the grid so type in shell. and then setup. in the following command prompt. (While the main prolog prompt is ?-, in the shell it will look like ?).
After the setup/0 has finished, you can exit the shell using either stop.,CTRL+D or CTRL+C then (a)bort at the prompt.
Identifying your Agent
At the top left of the grid, you will be able to see a coloured shape. This is your agent. For the first task in this exercise, you need to find a query that allows you to identify your agent and their current position and run it in the shell.
Create predicate m/1
The first step of moving around the grid world is defining the directions that we are able to move. They are n,e,s and w. For the first part of this exercise, you will need to define the predicate m(A) such that it is true when A is a valid direction.
Create predicate on_board/1
Next, We need to create the predicate on_board(+P) that tells us if a position P is on the board. Positions are stored as a compound term p(X,Y) where both X and Y range from 1 to the grid size inclusive.
TIP: You can use the predicate ailp_grid_size/1 to find the size of the grid.
Create predicate pos_step/3
For this step we need to find the new position after an agent has made a possible step (although we don’t need to check the validity yet!). The full predicate is pos_step(+Pos,+Dir,-NPos).
Create predicate new_pos/3
We are now able to combine the previous steps together to find the new position after a move has been made as well as to check that the move is valid. new_pos(+Pos,+M,-NPos) should be true if moving from Pos in direction M will lead to NPos and NPos is on the board.
Create predicate complete/1
The predicate complete(+L) should be true if the Length of L is equal to the number of cells in the grid. The size of the grid SHOULD NOT be hardcoded.
Create predicate spiral/1
The final part of this exercise is to implement the predicate spiral(-L) which will move the agent from the start position p(1,1) towards the center of the grid in a spiral pattern. L should be the list of steps that are taken by the agent to reach the center including the start position (You can test this using complete/1)
TIP: In order for the agent to actually move, you will need to use agent_do_moves(A,L) where A is the identifier of your Agent and L is a path that does not include your current position.
Exercise 2: Identity Loss – Part 1
For the next exercise, you will need to use a wikipedia API to uncover the identity of an actor based only on links from their wikipedia page. You will need to edit lab_identity_12345.pl.
Possible Queries
The following queries have been exported from the library code:
Predicate Meaning
actor(-Actor) return each possible secret actor identity (e.g. ‘Billy Bob Thornton’)
wp(+Title,-WikiText) connect to Wikipedia page with given Title and return its WikiText
wp(+Title) connect to Wikipedia page with given Title and print its WikiText
wt_link(+WikiText, -Link) return any Link contained in the given WikiText
agent_ask_oracle(+A, +Orac,+Qu,-Ans) This is used to question the oracle. If the Agent’s Question is link then the Oracle’s Answer will be a random link from the Wikipedia page whose title is the (name of the) secret random actor identity
test test if find_identity/1 successfully returns correct identity in all possible cases
How to run?
Run using swipl ./ailp.pl lab identity
The file lab_identity_12345.pl will automatically be consulted and should be the place that your work is done. There is no need to follow the steps to start the webserver this time as the grid world itself is not used.
Experiment with the predicates
Before you start to find the secret identity it is a good idea to familiarise yourself with the predicates. Can you find a query that stores all the links from a wikipedia page of your choice in a list?
Create predicate find_links_by_actor/2
It’s now time to create a predicate that finds all the links on a given actors wikipedia page. This predicate will take the form of find_links_by_actor(+Actor,-Links).
If you have made it this far then you are done for the week!